The present invention relates to a positioning control apparatus, and in particular to a positioning control apparatus suitable for head positioning control of a magnetic disk apparatus.
In a magnetic disk device used as an external storage device of a computer, a magnetic head is moved to a desired track on a rotating magnetic disk face and data recording and reproducing are conducted. In order to increase the processing speed of data access to the magnetic disk device, it is necessary to move a magnetic head to a desired track position at high speed and with high precision. As for conventional techniques of a magnetic head positioning control apparatus, there is, for example, one described in JP-A-4-000508. In this technique, a head position and a head moving speed are detected, and a speed trajectory (profile) for arriving at a desired position and a trajectory of a head drive current are generated on the basis of a deviation between the detected head position and a desired position. Feedback control is effected on a head drive current according to an error between a speed indicated by the speed trajectory and the detected head moving speed and values indicated by the head drive current trajectory. In a technique disclosed in JP-A-2001-135050, a function of conducting feed-forward control on a head by using an acceleration signal corresponding to a head drive current as an input is added to feedback control similar to that described above. As a result, over-muting is prevented from being caused by the feedback control.
A positioning apparatus shown in FIG. 3 is disclosed in Fujimoto et al., xe2x80x9cSeeking Control of Hard Disk Drive by Perfect Tracking using Multirate Sampling Control,xe2x80x9d The transactions of the Institute of Electrical Engineers of Japan, Section D, Vol. 120, No. 10, pp. 1157-1164, October 2000. If a target position Po used until a target position, which is not illustrated, is given in this apparatus, a trajectory generation section 31 first derives a time (seek time) taken until the target position is arrived at. Assuming that a control period of head drive is Tu, which is half of a track position detection period 2Tu, the trajectory generation section 31 derives a position trajectory Pt and a velocity trajectory Vt, which change in position at intervals of 2Tu, for implementing the above stated seek time. An acceleration generation section 32 calculates a feed-forward control signal Um by using the position trajectory Pt and the velocity trajectory Vt according to the following expressions                               U                      m            ⁢                          xe2x80x83                        ⁢            f                          =                                            1                              T                u                2                                      ⁢                          (                                                P                  t                                -                                  P                                      t                    ⁢                                          xe2x80x83                                        ⁢                    b                                                              )                                -                                    1                              2                ⁢                                  T                  u                                                      ⁢                          (                                                V                  t                                +                                  3                  ⁢                                      V                                          t                      ⁢                                              xe2x80x83                                            ⁢                      b                                                                                  )                                                          (        1        )                                          U          ms                =                                            1                              T                u                2                                      ⁢                          (                                                -                                      P                    t                                                  +                                  P                                      t                    ⁢                                          xe2x80x83                                        ⁢                    b                                                              )                                +                                    1                              2                ⁢                                  T                  u                                                      ⁢                          (                                                3                  ⁢                                      V                    t                                                  +                                  V                                      t                    ⁢                                          xe2x80x83                                        ⁢                    b                                                              )                                                          (        2        )            
where Ptb and Vtb are values of Pt and Vt calculated 2Tu before, and n is an integer that represents the number of periods from the seek operation start time, where one period is Tu. A model 33 is a model representing a control subject, and is given as, for example, a system including a double integral and a time delay. As for this model, a feedback model position signal Pf is calculated from a feed-forward control signal Um derived by the expressions (1) and (2). A difference between the feedback model position signal Pf and an actually detected position signal P of a control subject 35 is input to a position controller 34 as an error signal e. A feedback control signal Uh is generated by the position controller 34. The control subject 35 is controlled by a control signal D, which is the sum of the feed-forward control signal Um and the feedback control signal Uh.
In Shinsuke Nakagawa et al., xe2x80x9cMulti-rate Two-Degree-of-Freedom Control for Fast and Vibration-less Seeking of Hard Disk Drives,xe2x80x9d Proceedings of the American Control Conference Arlington, Va. Jun. 25-27, 2001, there is proposed a calculation method of a target position trajectory with due regard to mechanism resonance characteristics. A further erformance improvement is realized in the calculation method as compared with the above described method proposed by Fujimoto et al.
The technique of Fujimoto et al. and the technique of Nakagawa et al. use a feed-forward control system for causing the head position to track the calculated position trajectory and velocity trajectory, and a feedback control system for compressing the deviation between the head position and the target position trajectory. If there is not a difference between a current command value obtained from the feed-forward control system and the value of an actual current flowing through an actuator, then favorable tracking characteristics can be realized. When the moving distance of the head is long, the control signal attempts to flow a large drive current and consequently current saturation is apt to occur in the actuator, which drives the head. If a large difference occurs between the current command value obtained from the feed-forward control system and the value of the actual current flowing through the actuator, then the deviation between the head position P and the model position signal Pf for position feedback increases, and aggravation of the tracking performance caused by an anti-windup phenomenon cannot be avoided. Furthermore, it also poses a problem that the deviation between the model position signal Pf for position feedback and the head position P is increased by computation errors and numerical value rounding errors generated when calculating the feed-forward input.
An object of the present invention is to provide a positioning control apparatus that improves the technique of Shinsuke Nakagawa et al. and that prevents the control performance from being aggravated even when current saturation has occurred in the actuator or even when computation errors pose a problem.
In accordance with a first aspect of the present invention, there is provided a positioning control apparatus for moving a head that conducts recording and/or reproducing on a magnetic recording medium to a target position, the positioning control apparatus including: a trajectory generation unit for calculating a seek time required to move the head to a given target position, and a position trajectory and a velocity trajectory within the seek time every 2Ts, Ts being a sampling period of a position signal detected by a head position detection unit; a rigid body model and a dead time model of a head system ranging from outputting of a head drive signal to outputting of a detected position signal, inclusive of a head drive unit; a model control unit for calculating first and second model feedback control signals every 2Ts so as to cause a rigid body model position and a rigid body model velocity calculated by using the rigid body model to coincide respectively with the position trajectory and the velocity trajectory at a next sampling time point of the position signal, Ts being the sampling period of the position signal; a position control unit for calculating a feedback control signal based on a deviation between a model position for position feedback calculated by using the rigid body model and the dead time model and the detected position signal; a saturation detection unit for effecting detection to determine whether a drive current flowing through the head drive means is saturated; and a switching unit for setting an input control signal equal to the first model feedback control signal at an even-numbered sampling time point of the position signal, setting the input control signal equal to the second model feedback control signal at an odd-numbered sampling time point of the position signal, responding to the drive current being judged by the saturation detection unit to be not saturated by setting a model input of the rigid body model equal to the input control signal and outputting a sum of the feedback control signal calculated by the position control unit and the input control signal to the head system as the head drive signal, and responding to the drive current being judged to be saturated by setting the model input of the rigid body model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from a head acceleration corresponding to the drive current and outputting the input control signal or the head acceleration to the head system as the head drive signal.
In accordance with a second aspect of the present invention, there is provided a positioning control apparatus for moving a head that conducts recording and/or reproducing on a magnetic recording medium to a target position, the positioning control apparatus including: a trajectory generation unit for calculating a seek time required to move the head to a given target position, and a position trajectory and a velocity trajectory within the seek time every Ts, Ts being a sampling period of a position signal detected by a head position detection unit; a rigid body model and a dead time model of a head system ranging from outputting of a head drive signal to outputting of a detected position signal, inclusive of a head drive unit; a model control unit for calculating first and second model feedback control signals every Ts so as to cause a rigid body model position and a rigid body model velocity calculated by using the rigid body model to coincide respectively with the position trajectory and the velocity trajectory at a next sampling time point of the position signal; a position control unit for calculating a feedback control signal based on a deviation between a model position for position feedback calculated by using the rigid body model and the dead time model and the detected position signal; a saturation detection unit for effecting detection to determine whether a drive current flowing through the head drive unit is saturated; and a switching unit for setting an input control signal equal to the first model feedback control signal during a former half having (xc2xd)Ts of the sampling period Ts beginning with a sampling time point of the head signal, setting the input control signal equal to the second model feedback control signal during a latter half having (xc2xd)Ts of the sampling period Ts, responding to the drive current being judged by the saturation detection unit to be not saturated by setting a model input of the rigid body model equal to the input control signal and outputting a sum of the feedback control signal calculated by the position control unit and the input control signal to the head system as the head drive signal, and responding to the drive current being judged to be saturated by setting the model input of the rigid body model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from a head acceleration corresponding to the drive current and outputting the input control signal or the head acceleration to the head system as the head drive signal.
In accordance with a third aspect of the present invention, there is provided a positioning control apparatus for moving a head that conducts recording and/or reproducing on a magnetic recording medium to a target position, the positioning control apparatus including: a trajectory generation unit for calculating a seek time required to move the head to a given target position, and a position trajectory and a velocity trajectory within the seek time every 2Ts, Ts being a sampling period of a position signal detected by a head position detection unit; a rigid body model and a dead time model of a head system ranging from outputting of a head drive signal to outputting of a detected position signal, inclusive of a head drive unit; a model control unit for calculating first and second model feedback control signals every 2Ts so as to cause a rigid body model position and a rigid body model velocity calculated by using the rigid body model to coincide respectively with the position trajectory and the velocity trajectory at a next sampling time point of the position signal, Ts being the sampling period of the position signal; a position control unit for calculating a feedback control signal based on a deviation between a model position for position feedback calculated by using the rigid body model and the dead time model and the detected position signal; a saturation detection unit for effecting detection to determine whether a drive current flowing through the head drive unit is saturated; and a switching unit for setting an input control signal equal to the first model feedback control signal at an even-numbered sampling time point of the position signal, setting the input control signal equal to the second model feedback control signal at an odd-numbered sampling time point of the position signal, responding to an absolute value of a difference between the first and second model feedback control signals exceeding a predetermined threshold by setting a vibration compensation input equal to an average of the two model feedback control signals, responding to the absolute value not exceeding the predetermined threshold by setting the vibration compensation input equal to the input control signal, responding to the drive current being judged by the saturation detection unit to be not saturated by setting a model input of the rigid body model equal to the input control signal and outputting a sum of the feedback control signal calculated by the position control unit and the vibration compensation input to the head system as the head drive signal, and responding to the drive current being judged to be saturated by setting the model input of the rigid body model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from a head acceleration corresponding to the drive current and outputting the vibration compensation input or the head acceleration to the head system as the head drive signal.
In accordance with a fourth aspect of the present invention, there is provided a positioning control apparatus for moving a head that conducts recording and/or reproducing on a magnetic recording medium to a target position, the positioning control apparatus including: a trajectory generation unit for calculating a seek time required to move the head to a given target position, and a position trajectory and a velocity trajectory within the seek time every Ts, Ts being a sampling period of a position signal detected by a head position detection unit; a rigid body model and a dead time model of a head system ranging from outputting of a head drive signal to outputting of a detected position signal, inclusive of a head drive unit; a model control unit for calculating first and second model feedback control signals every Ts so as to cause a rigid body model position and a rigid body model velocity calculated by using the rigid body model to coincide respectively with the position trajectory and the velocity trajectory at a next sampling time point of the position signal; a position control unit for calculating a feedback control signal based on a deviation between a model position for position feedback calculated by using the rigid body model and the dead time model and the detected position signal; a saturation detection unit for effecting detection to determine whether a drive current flowing through the head drive unit is saturated; and a switching unit for setting an input control signal equal to the first model feedback control signal during a former half having (xc2xd)Ts of the sampling period Ts beginning with a sampling time point of the head signal, setting the input control signal equal to the second model feedback control signal during a latter half having (xc2xd)Ts of the sampling period Ts, responding to an absolute value of a difference between the first and second model feedback control signals exceeding a predetermined threshold by setting a vibration compensation input equal to an average of the two model feedback control signals, responding to the absolute value not exceeding the predetermined threshold by setting the vibration compensation input equal to the input control signal, responding to the drive current being judged by the saturation detection unit to be not saturated by setting a model input of the rigid body model equal to the input control signal and outputting a sum of the feedback control signal calculated by the position control unit and the vibration compensation input to the head system as the head drive signal, and responding to the drive current being judged to be saturated by setting the model input of the rigid body model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from a head acceleration corresponding to the drive current and outputting the vibration compensation input or the head acceleration to the head system as the head drive signal.
In accordance with a fifth aspect of the present invention, there is provided a positioning control apparatus, in which: a resonance model of the head system is added to the positioning control apparatus; the model position for position feedback is calculated by using the resonance model, the rigid body model, and the dead time model; when the saturation detection unit has judged the drive current to be not saturated, the switching unit sets a model input of the resonance model equal to the input control signal; and when the saturation detection means has judged the drive current to be saturated, the switching unit sets the model input of the resonance model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from the head acceleration corresponding to the drive current.
In accordance with a sixth aspect of the present invention, there is provided a positioning control apparatus, in which: a resonance model of the head system is added to the positioning control apparatus; the model position for position feedback is calculated by using the resonance model, the rigid body model, and the dead time model; when the saturation detection unit has judged the drive current to be not saturated, the switching unit sets a model input of the resonance model equal to the vibration compensation input; and when the saturation detection unit has judged the drive current to be saturated, the switching unit sets the model input of the resonance model equal to a signal obtained by subtracting the feedback control signal calculated by the position control unit from the head acceleration corresponding to the drive current.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.